Structure and method of operation of heating furnaces



Aug. 12 1924. 1,504,656

W. TRINKS STRUCTURE AND METHOD OF OPERATION OF HEATING FURNACES FiledJuly 1'7. 1923 4 Sheets-Sheet 1 HWEA/TOR WITNES$ES .M Li

Aug. 12 1924.

W. TRINKS STRUCTURE AND METHOD OF OPERATION OF HEATING 'YFURNACES 4Sheets-Sheet 2 Filed July 17. 1923 1 Hdi 0 INVENi'OR Aug. 12. 1924.

W. TRINKS STRUCTURE AND METHOD OF OPERATION OF HEATING FURNACES FiledJuly 17, 1923 4 Sheets-Sheet 4 "H m-h INVE/V 7'01? WITNESSES Patented l2UNITED STATES.

wnmam) TRINKS, or ,PITTSBURGH, PENNSYLVANIA.

STRUCTURE AND IMIIBTHOD OF OPERATION OF HEATING-FURNACES.

Application filed "July 17,

To all whom it may concern:

. Be it known that I, WILLIBALD TRINKS, residing at Pittsburgh, in thecounty of Allegheny and State of Pennsylvania, a citizen of the UnitedStates, have invented or dis-" covered certain new and usefulImprovements in Structures and Methods of Operation of Heating Furnaces,of which improvements the following is a specification. My inventionrelates to improvements in the structure of and in the method ofoperation of heating furnaces. It includes improvements uponthedisclosuresof an application of Kernohanand Lochhead, for United StatesLetters Patent, filed October 29th, 1920, Serial No. 420,377, and of anapplication filed by me June-22nd, 1923, Serial No. 647,008. In my[prior application last alluded to I speak of a highvelocity jet as a.fl0w-impelling agent, and claim a specific furnace and its method of oeration, in which such a jet may be emp oyed. In this application Ishall mo re minutely describe that jet and claim-1t 1tself, as the a cutfor the purpose indicated.

My invention," as inthe sequel will appear, is applicable generally toheatm furnaces' and their operation, but. I shal first describe it inthe particular application in which I have developed it, the.applicatlon,

namely, to an open-hearth steel furnace.

In the accompanying drawings, Figure I is a view in approximatelyhorizontal section, on the plane indicated by the broken line I-I,Figure II, of an open-hearth steel furnace, 'in which, and in theoperation of which, my invention is present and may be carried out.Figure II is a view 1n vertical section of the same furnace, on theplane indicated by the broken line IIII, Figure I. Figures III, IV and Vare views in vertical section, III and V through ingot-heating furnaces,IV through a billet-heating furnace, and in these figures theapplicability of my invention to these furnaces, various in kind, isillustrated. Figure VI is a view in lon itudinal section and to muchlarger scafis of a certain-nozzle, which I preferably em loy, ashereinafter explained.

ferring first to Figures I and II, the furnace includes the usual hearth1, upon which the charge is borne and where the essential refiningoperation takes place. Producer gas, preheated in the regenerator (notshown) flows through passageway 3; thence 1923. Serial N0. 652,061.

it rises throu h vertical passageway 6, and enters from t e rear themedially arranged downwardly inclined tunnel port 4. Through this portthev stream of gas is carried into the furnace chamber. Atmospheric air,preheated'in the air regenerator (not shown),

flows through passageway. 2; thence it rises in divided flow through twovertical passageways 7 and 8, symmetrically arranged one on either sideof the mid-line of the'furnace, and enters from the rear the downwardlyinclined port 5, over-arching port 4. Through "this port air is carriedinto the furnace chamber. Ducts 9-and 10 lead from air .passagewa s .7and 8 and open into port 4, Of these ucts it is to be observed that theyare symmetrically arranged, and that the flow through them will besymmetrical with respectto the mid-line of the furnace; they extendobliquely forward, and the streams flowing through them will convergewith the stream flowing directly through the tunnel port '4; they openinto the tunnel port 4 at an intermediate point inthe length thereof,and the'conver ing streams will min le before the mout of the, port isreac ed. Nozzles 19 and 20 are provided, through which com iressed airfrom a supply P1 e 21 may be lown in jets forwardly throng ducts 9 and10. In supply pipe 21 is a valve 23 for regulating the flow, and

conveniently a secon valve 22, for cutting off the flow entire] "Theshowing aflXirded in Figs. I and II will be understood to bediagrammatic, and particularly in these respects: The ducts 9 and 10 areshown as rectangular in cross section and uniform in dimensionsthroughout their extent. Manifestly' they may be articularly shapedaccordin to the te'ac ing of neumatics, to afford in highest degree theefi'ect described; the nozzles'l9 and 20 shown diagrammatically as meretapered terminations of the feed pipes protruding into the ducts, may beelaborated and refined inform; they may be made of the multi le-jettype; they may in position be. so re lated to the form of the ducts asbest to achieve their effect again, the openings through the walls ofpassageways 7 and 8, through which the nozzles 19 and 20 are shown to bemovable are, in order that the structure may be clearly understood,shown diagrammatically as greater in dimensions than in actual buildingthey would be.

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- the arrangement here described is a preferred, but not a limitingfeature.

I have just said of the nozzles. 19 and 20 that they may be elaboratedand refined in form. And here I pause and anticipate a description ofmode of operation to remark that 'ets of compressed air are projectedlongitu inally in ducts 9 and 10 at the intake end of the furnace toinduce flow of streams of air from uptake passageways 7 and 8 throughthese ducts 9 and 10 and into port 4. My furtherand more specificinvention in respect to these ducts is illustrated in Fig. VI, where Ishow a nozzle of a convergentdivergent shape, sometimes called a DeLaval nozzle. Inspection of Fig. VI will in view of the foregoingstatement make plain the feature here dwelt upon.

The convergent-divergent nozzle has this capacity,that if gas underpressure exceeding a critical minimum (for air discharging into theatmosphere this critical minimum is a pressure of approximately twoatmospheres) be jetted through it, a very high jet velocity may beattained. From an ordinary convergent nozzle jet velocity is limited tothe velocity .of sound in the medium employed. This velocity is for airabout 1,100 feet a second. Froma convergent-divergent nozzle jetVelocities of 1500 feet a second in air and even higher may be got.

The advantage of this high-velocity nozzle to my invention is this: Ifthe compressed air jetted through nozzles 19 and 20 be unheated it willon mixing with the air drawn from passageways 7 and 8 effect somecooling of the streams, and there is apoint beyond which such coolingmay not advantageously be carried. On the other hand, it is an economicadvantage if the air jetted from-the nozzles may. be used in unheatedcondition. Increased velocity of jet means that the same flow of heatedair from passageways 7 .and 8 through ducts 9 and 10 may be got withjets of diminished weight.

Accordingly, the employment of convergentdivergent nozzles means that Ican use'unheated air under conditions which otherwise would requirepreheating,-preheat ing, that is, of the compressed air etted from thenozzles. I

I have shown the compressed air supply pipes 21 at opposite ends of thefurnace, together with the connections which terminate in nozzles 19 and20, to be suspended, as by chains 24, and it will be understood that bysuch means the nozzles 19 and 20, positioned as shown at'the intake(left hand) end of the furnace, may at the outtake (right hand) end beswung aside, away from the deleterious influences of the outflowingproducts of combustion. As an alternative ex edient, these pipes may bestationaryan the nozzles water-jacketed--an expedient so well known inthe general field of furnace structure as to require no illustration.

As shown in the drawings, the furnacereversing instrumentalities will beunderstood to be arranged for the inflow .of gas and air at theleft-hand end and for the outflow of products of combustion at therighthand end. At the left-hand end of the furnace the valve 22 in thesupply pipe 21 will be understood to be open, and at the righthand endthe corresponding valve will be understood to be closed, and at that endthe pipe itself is shown to be retracted and the nozzles 19 and 20withdrawn beyond the walls of vertical passageways'7 and 8. Gas and airare entering through the ports at the left-hand end and are burning in aflame which sweeps from left to right, and the products of combustionare escaping throu h the ports and passageways at the rightand end. Atproper intervals of time the furnace is reversed and, incidentally toreversal, the pipe 21 and nozzles 19 and 20 at the right-hand end whichhad of the furnace requires no illustration, and

I have not sought to afford illustration of it.) The degreeof opening ofvalve 23 may, if desired, be diminished as operation upon'a givenfurnace charge progresses, to the end that at the beginning the flamemay be relatively short and sharp and toward the end relatively long andlazy.

In the operation of open-hearth furnaces ascommonly conducted hitherto,the draft through the furnace has. been relatively feeble, andcombustion has been imperfectly controlled. This has been particularlytrue of furnaces fired with producer gas. In the operation of thesefurnaces the air ordinarily has been drawn through the air rcgeneratorsand into the furnace merel by the stack effect of the regenerators anthe uptakes. The gas flowing from the producer and through the gasregenerator and thence to the furnace has been commonly subjected onlyto such pressure as is incident to its delivery from the producer. Insome cases a blowing fan has been placed in the stream of the air supplyto the furnace, but there is a practical limitation upon the building upof the pressurethere. \Vhen the pressure exceeds a small amount, leakagethrough the masonry of the furnace structure becomes too great. It isdifficult. be-

cause of expansions and contractions inciin order to produce a sharpflame, require that the ports be relatively narrow, and narrow ports donot afford at the discharge end of the furnace unhindered exit for theproducts of combustion. (It is of course to be understood,and thecondition has already been alluded to,that in ordinary openhearthoperation the flow of the flame is periodicallyreversed, and duplicatesets of ports at opposite ends of the furnace serve alternately to leadin'the gas and air and to lead out the vastly greater volumes of hotproducts of combustion.) Because of these difliculties chiefly, and inspite of various relief projects, open-hearth operationas a matter ofpractice has been limited to low rates of flow of, air'and of gas and tothe generation of a consequent long and lazy flame. This flame is stillburning when it reaches the ports at the outgoing end of the furnace andcombustion continues through the ports and even down into theregeneratorsa state ofthings both wasteful and destructive. A roposal touse dampers for,

reducing the e ective size of the passageways at the intake end of thefurnace, with the end in view of increasing there the velocity of flow,involves complication of structure, and the dampers, when present,

absorb a great deal of heat. v

In the furnace of F ig's, I and II,'while operation is in-progres s,compressed air is blown through nozzles 19 and 20 into ducts 9 and 10.This compressed air may, as has been explained, be preheated or not, as

found desirable 'or convenient, and if preheated, the preheating may becarried to any desired degree. But, as;.I have explained, the necessityfor preheatin may within wide limits, be "avoided. The ets of airissuing from the nozzles have high velocity-from GOO-to 1509 feet persecond or more,--a matter conditioned upon the actual pressure of the"supply and upon the shapeof the nozzle and the s'ize and shape of theorifice. This highvelocity jet entrains hot air from the uptakepassages7 and 8,-and induces a'flow ofair through ducts 9 and 10 intothe stream of gas ad vancing through port 4. Thus the entering stream ofair isdivided;-one portion. is directed into port 4, where it mingleswith the gas before entering the furnace chamber;

the other portion flows unmingled through port 5 into the furnacechamber. The relative value of these two portions 7 of the stream ofentering air is variable and responsive to the degree of opening ofregulatin valve 23; if that valve be closed complete y, all of the airwill, under suchcon ditions as usually obtain, enter the furnace chamberthrough port 5and*,indeed, because of the fact that usually the gasadvances to the furnace under pressure greater than that of the air,there will be some back opened Wider.

tieth to one sixth by weight of the air flow-' iug in ducts 9 and 10 isthat which flows from the nozzles; the rest is drawn in from the streamsof air rising through uptakepassag 7 and 8. By roperly proportioning insize ports 4 and 5, passageways 7 and 8, and ducts 9 and 10, it ispossible by the means described to divert through ducts 9 and 10 intoport 4 any "desired fraction of the streams of air rising through uptakepassageways 7 and 8 Indeed, it is possible so to divert substantiallythe whole of these streams; ordinarily it is not desirable in operationto go so far as that, but it is-preferable toallow some air to enter thefurnace through port 5. I

'When valve 23 is nearly closed the flame is long and lazysuch a flamein fact as is usual in open-hearth operation as commonly conductedhitherto; if the valve 23 is opened wide, the flame is short and sharp.

Any desired sharpness of flame may be ob tained by movement of theregulatingvalve 23. A shorter sharper flame than that usual in theopen-hearth operation is desirable; combustion; is then completed withinthe furnace chamber, where alone combusmay be relatively short-andsharp, and toward the end relatively lon and lazy. -As has been intimateI 0. not intend ordinarilyto resort to .special means for building 'uppressure on air or gas on'the intake end of the furnace nor to specialvmeans for drawing the products of combustion out from the outgoing end.Nevertheless, the practice of my invention does not forbid the use ofsuch ancillary apparatus, if for any reason it be found desirable.

The streams of air entering port '4 through ducts 9 and 10 producecombustion in port 4, to the extent that the air and gas mix. Mixture,however, is not complete until the gases have just left port 4 on theirway to the furnace; Inconsequence, com-v bustion in and just beyond theopening from port 4 is so rapid that an-extremely high.

greater. than issue from the jets) from the air passageways 7 and 8through ducts 9 and 10 into port 4. Furthermore, by the I use of thejets of compressed air, this proing air or 45 jecting of streams of airthrough ports 9- and 10 .is attained without subjecting the furnacestructure to augmented'pressure 1n the regenerators or in the air uptakepassageways' 7 and 8, and without resort to dampers.

I have consistently spoken of the substance projected through nozzles19and 20 as compressed air, andcrdinar ly'compi'essed air will be best;air is requisite to combustion in ordinary practice, and is onecomponent of the combustiblemixture within the furnace chamber. Butmanifestly the jetmight be constituted of some other fluidof steam, forexample, or of oxygen, or of a substance which, while not entering intothe act of combustion, still serves mecham ically, to divert thesubstance of one of the two streams through the ducts 9 and 10.1nto

the other stream.

The arrangementof ports and passage -ways might be reversed, and gasrising through passageways7 and 8 diverted and projected into the airadvancing from passageway 6 through port 4. a

The use of a high velocity jet for entrainnaces is not limited to theuse of auxiliary ports 9 and 10, as shown in Figures I and II. A jettraveling at high velocity entrains and induces the surrounding fluidsby VlS cous drag and forces them to travel in the direction of the jet.The velocity of the et slows down as more and more'of the surroundingfluid is 'entrained.- no matter whether that fluid be air, gasor vaporsuch as vaporized oil or tar; The jet has a double action, firstitentrains, accelerates, and GIYQS direction, and, second, it mixes thefluids which are entrained.

By experimenhl'have found that a'high velocity jet spreads fromthenozzle entraining the surrounding fluid, making a total cone angle ofabout 26 degrees if flowing in a reasonably open space. Within the jetthe total momentum remains approximately constant at any cross sectionalong Y the flow.

fuel in heating or'melting fur-l No inatter whether the jet entrainsfluid in a duct or whether it does so in a reasonably open space, suchas the main chamber of a furnace, the outstanding fact remains that thejet issuing at very high velocity from a high pressureconvergent-divergent nozzle has much more directing and entraining powerthan a jet which is discharged from a convergent nozzle and that, bythis very fact,

the use of a high velocity jet becomes possible when the ordinary jetwould be a failure because of too much mass of the entraining Thefurnace illustrated in Figures I and II is an open-hearth furnace,designed for the use of gas as fuel and, specifically, producer gas.Figure-III shows diagrammatically a heating furnace for ingots, the fa-;miliar pit furnace provided at .a blooming mill. In it ingots I areshown restin on the hearth 301 of the furnace chamber. urnaces for thispurpose are ordinarily regenerative furnaces and admit of a considerablelatitude in structure and considerable modification in mode ofoperation. The furnace shown will however serve as a typical fur mice ofthis general sort. In this particular instance it w ll be observed thatit is the air only which is regenerated in regenerators 30, while thefue(which in this instance will-be understood to be gas relatively richinquality.-coke-oven gas,for instance) is introduced through pipe 31 intothe stream of regenerated air as it advances to the furnace port.Astructure is built upon the wall of the passageway fromregenerator tofurnace port which in mill parlance is called a .doghouse. Within thisdoghouse, as clear ly a pears, is formed a b -pass 32, through whic afraction of thee vancing stream of air is shunted. Into this b pass openfuelsupply pipes 327 '(the'num er and arran ement may be such asdesired, ordinaril t e arrangement will be symmetrical wit respect tothe line of flow) The fuel introduced will ordinaril be gas; itmay,however, be powdered car naceous material borne on a gaseous stream.Pipe 319 carries compressed air (or equivalent fluid). It extends intothe byass 32, and from it a ct is projected in the ine of flow through tis bypass and in the "direction of the furnace chamber and such jetserves, as in the othercases already descr bed, to impel flow throu 11the bypass and throu h the port, into tIi'e furnace. The structure.iflers from the structure of Figures 1 and II, in that the jet-impelledbranch of the stream reunites with the other branch ,and the unitedstream enters thrpugh the single port into the. furnace. This is avariant which may be noted in passing. I have said that a gas ofrelative richness will in ordinary contem lation be introduced throughthe fuel-supp y ipe.31 atthe inlet end of the furnace. Tiis gas may benatural gas, for example, or cokeoven gas, or even producer gas, or 1tmay be a gaseous stream carrying a burden of powdered carbonaceousmaterial. From what has gone fore the operation will be fullyunderstood.

Figure V serves merely to indicate how the same essential invention maybe appliedmiliar construction. Uponthe furnace wall is built a doghouse,into which doghouse there opens an uptake passageway 407 for air, whichit Iwiltbe understood may lead The chamber 404 within the doghouse, sosupplied with air, opens to the furnace chamber. Into chamber 404 fuelis intro- 'duced,.as is indicated at 427, and nothing more need be saidabout fuel than to remark that fuel of any preferred character withinthe range already noted may be introduced I in the manner and by themeans already de:

scribed. A compressed-air pipe 419 dis-'- ch'arges a jet in the line offlow of airthrough the chamber 404, and into the furnace chamber.

Mention of a recuperator gives occasion to note a further advantage ofmy invention. A recuperator is .a heat exchanger in which streams ofentering air glor gas) and of outflowingflaming gases or ot productsof-combustion flow 1n contiguous passage: Ways, separated by aheat-penetrable partition wall. This'wall ordinarily is .a thin wall ofbrickwork. Draft through the furnace is ordinarily maintained by astack; and in the recuperator, while the stream of air flowing on oneside of the partition is under a pressure slightly in excess of that "ofthe atmosphere, the stream of hot gas flowing on the other side of thepartition is, in consequence of the draft condition established by thestack, under a pressure appreciably less than atmospheric. A thin wallof brickwork'is liable to deterioration and leakage, and with inequalityof pressure on its opposite sides, leakage means disturbance suck thepreheated air out of the recuperator except by its own buoyancy which,in some cases, has been augmented by the'action of a fan at the cold airinlet of the recuperator.

" In any such case there is a pressure greater than atmospheric eitherthroughout the whole! length of the air passageways in the recuperatoror at least in that portion nearest to the hot-air outlet. Theapplication rom a recuperator or from a regenerator.

of my invention 'now described toa furnace whose air supply ispreliminarily heated in a recuperator achieves a proper firing of thefurnace without the attendant necessityof an unbalancing of pressures inthe recuperator; the suction effect of the jet in the air passagewayleading to the furnace is to reduce the pressure of the entering air inthe recuperator to substantially that of the products of combustionflowing out through the recuperator to the stack. Consequently, wear andtear does not bring about that loss in efficiency just pointed out.

In describing the structure ofthese Figures III, IV and V I have said,generally, that the jetis ordinarily of compressed air,

and it ordinarily'will be, but it is to be understood that I am notlimited tothe use of compressed air, in view of what I have alreadysaid, m invention is embodied in the provision of a jet of fluid. Withthis brief definition of parts, it is believed that the structure andoperation ofthe furnace of gigure III also will be clearly understoo Allthat was said with reference to the furnace of Figs. I and II concerningvariations'in and refinements of structure; concerning the nature of thefluid projected from nozzles 19 and 20, and concerning its pressure andtemperature, and the effects of variation in these matters; all that wassaid concerning draft conditions maintained and means of maintaininthem, will be understood to be applicab e to the furnaces of FiguresIII-V and their operation. What has been said concerning pressure andtemperature of fuel will be understood to be applicable generally in theoperation of the furnaces described.

Reviewin the structures of all of the figures, it wil? be seen thatthere is throughout a chamber which, varying in detail, possessesconstant characteristics. I allude to the chamber 4 of Figures I and II,304 of Figures III and V, and 404 of Figure IV. In the ensuing claims Iuse in some cases the term port, in some cases the term mixing chamber.It will be understoodthat the varying phrase merely lays emphasis uponcertain characteristics of this same structural element, and neitherterm is used in an specifically limiting sense.

I have i ustrated a considerable latitude in modification of structure,and in method of operation.- In so doin I have not intended to limit therange 0 permissiblelatitude, but to indicate rather that the field iswide within which my invention may be herein described which consists inmaintainingya passageway for such preheated .air

leading to the furnace chamber and in projecting into such passageway aflow-inducmg jet of compressed gas at a velocity ex ceeding that ofsound; and causing fuel to mingle in the stream.

2. In the operation of a furnace -usin preheated air for combustion themetho herein described of impelling the flow of air to the furnacechamber which consists in that of sound, and means foradmitting filesubstantially as described.

to the induced stream, substantially as described. W

4. In a heating-furnace structure the combination with a furnace chamberof an air passageway leading thereto, a conduit for compressed gasprovided witha convergent-- divergent nozzle arranged within said passageway and meansfor admitting fuel to a stream of air flowin in. said v5. In he structure of a heating furnace using preheated air forcombustion the com- ;in sai passageway,

bination with a passageway forpreheated air leading to the furnacechamber, a conduitfor compressed gas provided with a converent-divergent nozzle arranged withpassageway, substantially asdescribed.

6. In a heating-furnace structure the combination with a furnace chamberprovided with an intake passageway for air and an outgoing passagewa forproducts of combustion, means for rawing the products of combustionthrough the outgoin passageway and means for projecting a ow-inducingjet of fluid at a velocity exceeding that of sound within the intakepassageway, substantially as described.

7. The method herein described of firing a furnace which consists inestablishing conditions of low-velocity flow through the furnace as awhole and at the intake end increasing locally the flow to a flow ofhigh welocity by projecting into the flow a jet of fluid at a velocityexceeding, that of sound.

In testimony whereof I have hereunto set my hand.

WILLIBALD TRINKS. Witnesses:

FREDERICK L. JENKINS, JOHN C. CARR.

